The applicant filed an application for patent on Jul. 7, 1990 in China and the patent right was granted to it thereafter, the title of the invention being "A GAS-LIFT OIL PRODUCING DEVICE" and the patent number being 90209934.5. The said device comprises a conventional gas-lift unit and a ball-control mechanism, makes a slug flow in the lift pipe with gas column mixed with well fluid being separated by feeding special gas-lift-balls at regular intervals so that the gas energy can be used to it's maximum and the injection-production ratio is reduced, producing depth is increased, therefore, the gas-lift efficiency is improved.
The ball-control mechanism consists of motor, gear bank, screw rod, oil-gas-ball separator, ball-control wheel, circular-cylinder-shape filter screen, oil-gas-ball inlet pipe and valve, high pressure gas inlet pipe and valve, oil-gas outlet pipe and valve, gas-ball outlet pipe and valve. The mechanism is of bilateral symmetry (left and right). The spiral direction of the left screw rod is opposite to the right one. A valves are connected with the pipelines and the shell of the oil-gas separator. Each pair of valves is connected with the gears and screw rod.
After high pressure gas from high pressure valve goes into the separator, the ball-control wheel turns under the force of the gas flow, and passes the gas-lift-balls into the gas-feeding pipe, forming a kind of flow structure of gas column separated with the gas-lift-balls. When the motor rotates clockwise, the screw rod will open the valve on the left and close the valve on the right. When the left valve opens, oil and gas and ball go into the left separator, with oil and gas going into the oil-gas outlet pipeline through the filter screen. When the left separator is filled with the balls, the motor begins turning anticlockwise. The right valve opens and the left valve closes. When the right valve opens, oil and gas and ball go into the right separator, with oil and gas going into the oil-gas outlet pipeline through the circular-cylinder-shape filter screen.
On May 13, 1994, the applicant filed an application for patent ("THE MULTIFUNCTION BALL-CONTROL DEVICE"), which was improved on the basis of the above-mentioned device. A patent was granted to it and the patent number is 9421188.5. The device takes advantage of the transmission and controlling mechanism and the bilateral symmetry of the above-mentioned device. In this ball-control device, the gas-lift-balls are separated by filter screen, the speed-regulating motor is used, the gear bank is used to control the spiral ball feeder which controls the balls delivery. And also, a spiral oil ditch with some small holes on it was designed, there is a baffle at the end of the oil ditch, on the top of which a separation cap is located for separating gas and oil. Nevertheless, the improved device has the following shortcomings: 1) the structure is complicated and expensive because of using the motor and gear bank and screw rod to control the two shells; 2) the safety degree is reduced and the investment enlarged because of the high pressure of 8-12 Mpa that the two shells have to be subjected to when injecting gas; 3) the feeding of gas and balls is not continuous, therefore, the pressure fluctuates because the two shells send out and receive balls and separate oil and gas respectively, and also, regular tank change must be proceeded; and 4) it is somewhat difficult to operate because of the bilateral symmetry structure. So, to some extent, the above two patents are difficult to be put into practice.